It is proposed to study the structural aspects of protein allosterism in human hemoglobin by exploiting the power of X-ray crystallographic methods to image protein conformation on the atomic level. In particular, It is proposed to elucidate the structure of hemoglobin H (beta 4) and to compare it with the structure of hemoglobin A (alpha 2 beta 2) in an effort to identify the intersubunit contacts which are vital for the proper functioning of hemoglobin A. A new method for directly determining the approximate pK values of titratable residues is described and shown to be feasible. It is planned to use this approach to identify the residues responsible for the unassigned portion of the alkaline Bohr effect. The interaction CO2 with deoxyhemoglobin will be studied under a variety of conditions. The effect of 2,3-diphosphoglycerate binding on the tertiary structure of deoxyhemoglobin will be studied in detail at high resolution. The structural reasons for the ability of inositol hexaphosphate to rejuvenate the functional properties of carboxypeptidase A - digested hemoglobin will be sought. The binding of drugs of potential value to the treatment of sickle cell disease will be studied in order to determine the structural basis of their action.